1. Field of the Invention
The present invention relates to the monitoring and control of turbomachinery and more particularly to an electromagnetic, non-intrusive sensing system.
2. Description of the Related Art
Currently, within the fields of jet engines, rocket engines and rotary engines, blade/impeller/gear elongation, bending, twisting, shaft travel, runout, torque, horsepower and disc precession are generally not measured in real time. Thus no real-time data is provided to detect the blade/impeller/disc degradation and imminence of blade/impeller/shaft rubbing, which can cause shearing of housings, explosions in flammable fluids or instability of the disc/shaft that can cause catastrophic disc/shaft fracture. Currently, turbines are redlined for safety, based on a single-point real-time gas temperature measurement, not the blade thermal or fatigue survivability limit. Since the exact blade temperature cannot be derived from gas temperature, the threshold temp is usually set at a lower value for safety and blade life reasons, thus reducing the turbomachinery potential efficiency and power output. Current pump designs allow a large impeller gap to prevent hazardous impeller rubbing, causing pump inefficiency. In addition, accelerometers are used to presumably detect some of these failures. However, accelerometers have not been able to detect all these failures consistently, and even occasionally have resulted in false alarms.
Currently, to prevent the above-mentioned failures, scheduled manual intrusive inspections are performed, using borescope, shaft travel gages, filler gages, radiographic films, dye penetrants, eddy current inspection, etc., that require laborious disassembly and subjective interpretation.
To prevent blade damage, the turbines have been redlined at lower temperatures, sacrificing valuable thermodynamic efficiency or maximum power. Similarly, the pumps have been designed with larger gaps to prevent catastrophic impeller rubbing, again sacrificing efficiency.
Isotech, Inc., of Horsham, Pa., markets a Metal Motion Sensor/Encoder that has the ability to sense metals in motion in such cases as gear speed applications through a non-magnetic stainless steel wall. However, the Isotech device requires electrical excitation which is undesirable in aerospace propulsion systems because it may potentially result in a catastrophic explosion. Such an explosion may result if the wire leads therein become exposed to internal turbine gases. Furthermore, this sensor has a very low frequency response.
U.S. Pat. No. 4,741,203, issued to D. O. Willaman et al., discloses an inspection device which permits inspection of the interior of a turbine for metal integrity. The inspection device is mounted on a sensor assembly that engages a turbine blade and rests on the turbine disc. Metal integrity sensors are mounted on the sensor assembly and inspect various areas of turbine blades and turbine rotor steeples. The associated coil assembly provides a coil of wire and magnetic shielding which improves the sensitivity of the metal integrity sensors. The associated method provides for proper positioning of the apparatus and inspecting the turbine for metal integrity. This device is positioned within the interior of the turbo machinery and is therefore intrusive and undesirable.
U.S. Pat. No. 4,884,071, issued to M. A. Howard et al., discloses an improved wellbore tool for coupling to a drill string at a threaded junction and adapted for use in a wellbore during drilling. A sensor is disposed in the wellbore tool for sensing a condition and producing a data signal corresponding to the condition. A self-contained power supply is disposed in the wellbore tool and coupled to the sensor for providing power to the sensor as required. The Hall Effect coupling transmitter means is carried by the sensor and transmits data from the Hall Effect coupling transmitter means to a Hall Effect coupling receiver carried by the drill string and disposed across the threaded junction from the wellbore tool. Data is transmitted across the threaded junction without requiring an electrical connection at the threaded junction. This device requires an electrical circuit and electrical excitation that may result in a catastrophic explosion.
U.S. Pat. No. 4,972,332, issued to B. L. Luebbering et al., discloses an apparatus for use on electronically controlled fuel injection systems. It senses speed, angular position, and direction of rotation using a single Hall effect type sensor. A disk element is fixedly connected to and rotatable with the camshaft of an internal combustion engine. The disk element includes a plurality of circumferential zones of substantially identical length with each zone having first and second areas. A first portion of these circumferential zones has first and second areas which are substantially different in length than the first and second areas of a second portion of the circumferential zones. Accordingly, the sensor delivers a signal which has a frequency directly related to the instantaneous velocity of the disk element, but that varies in pulse width in response to the first and second portions of the circumferential zones. A microprocessor operating under software control detects the instantaneous angular position and direction of rotation of the disk element by locating the second portion of the circumferential zones and the order in which they are received. The U.S. Pat. No. 4,972,332 apparatus measures speed and position of the rotating system as a whole and doesn't assume individual blade health.
U.S. Pat. No. 5,304,926, issued to M. T. Wu, discloses a position sensor having two magnetically sensitive devices associated with a magnet. The sensor is disposable proximate a rotatable member having at least one discontinuity in its surface. The two magnetically sensitive devices, such as Hall effect transducers, each provide output signals that represent the direction and magnitude of the magnetic field in which its respective transducer is disposed. An algebraic sum of the first and second output signals from the magnetically sensitive devices is provided as an indication of the location of the rotatable member that is disposed proximate the sensor. This device is positioned within the interior of the turbo machinery and is therefore intrusive and undesirable.
U.S. Pat. No. 5,552,711, issued to T. Deegan et al., discloses a method for determining when combustion cans or turbine blades are failing in gas turbine engines. It measures the specific ions emitted by hot spots of can and blade material when they have failed or are failing. The invention relies on the electromagnetic energy radiated by ions that are created as combustion gas erodes and ionizes the materials in these hot spots. Acceleration by the earth magnetic field and by acoustic and mechanical forces normally present in combustion machinery cause these charged particles to radiate identifiable electromagnetic emissions. The frequency of the radiation, being a function of the charge and mass of the particles, allows free ions in the exhaust stream to be identified. The device operates by measuring the electromagnetic spectrum and relating detected frequencies to the mass of the ions from can liner and blade materials. This detects the erosion of turbine/turbomachinery elements and does not detect fatigue or fracture of an element of the turbopump.
U.S. Pat. No. 6,247,900 B1, issued to C. A. Archibald et al., discloses an accurate and low cost sensing apparatus for a swash or wobble plate compressor that provides a repeatable measure of compressor speed and stroke. The apparatus includes a sensor module and a stroke sensing circuit. The compressor has an outer housing formed of aluminum or other non-magnetic material, as is customary in automotive air conditioning systems. The sensor module includes a magnetic field responsive sensor such as a Hall Effect or magneto-resistive (MR) sensor, and is attached to the periphery of the housing in proximity to a reciprocating ferrous element such as a bushing shoe on the swash or wobble plate assembly. The sensor produces a quasi-sinusoidal output voltage signal having a frequency proportional to compressor speed, and the stroke sensing circuit determines the compressor stroke by band-pass filtering, amplifying, and peak detecting the signal. This apparatus cannot provide blade-by-blade health information for rotary machinery.